The battery heater systems and methods described herein are in the field of battery devices. More specifically, the systems and methods disclosed herein are in the field of heaters for batteries for use in any aircraft, vehicle, mobile, or stationary devices exposed to extended cold temperatures. The systems and methods related also to aircraft batteries and internal heaters that are integrated into aircraft batteries. The systems and methods also relate to a self-powered battery heater system where the battery heater system is powered by the battery itself.
Batteries used to start vehicles such as aircraft and other heavy equipment may be required to produce significant current to support the starting and operation of the vehicle in which they are installed. Similarly, batteries used to power stationary or mobile devices, such as computers, laptops, mobile phones, and other electronic equipment, may need to operate in cold environments. When the vehicles or other devices are located or operated in cold environments, the batteries may become cold-soaked to the ambient temperature of the environment during periods when the vehicle is not in use. In some cases aircraft may be exposed to temperatures down to −45 degrees C. for extended periods. Batteries at these cold temperatures may be incapable of performing properly if they are used to attempt to start an engine, for example, because of frozen electrolyte or other effects of the low temperature.
Typically, when an aircraft will be exposed to such low temperatures for an extended time, the batteries may need to be removed from the aircraft and placed in a temperature-controlled environment to prevent electrolyte freezing. Aircraft batteries may be difficult to remove and reinstall in an aircraft, especially by personnel wearing cold weather clothing and gloves as would typically be required.
If it is impractical to remove the battery, the battery will get so cold that its electrolyte will freeze. When frozen, the electrolyte's viscosity will increase and will create a high internal resistance in the battery which resists the flow of Lithium ions and electrons necessary to sustain a high voltage and continuous current needed to start an aircraft engine or power a heater. In such situations, an external power source, such as a ground power cart, is necessary to provide electrical power to operate heaters provided for the battery, which may be internal heaters. Such external power sources may not be available at small airports or remote cold weather locations. If an external power source with a higher sustained nominal voltage (e.g. 28V) is available, the battery heater system will not need to employ any time, voltage, or duty cycle-based algorithm and can operate normally at full power up to the target temperature.
The dependence on either preventing electrolyte freezing or an external power sources is due to the assumption that the heater will operate at a consistent power level at its nominal voltage and current requirements. Furthermore the heater is operated using control logic focused on reaching and maintaining a target temperature. The inventive heater system and methods described herein are designed to use the limited power available in the cold batteries to self-heat.